Posts Tagged ‘capacitors’
what is electricity? part 3: capacitors, dielectrics and confusion
an electrophorus, apparently
Canto: I’ve found a useful website on the history of the capacitor, which tells us that the term condenser was an early term for a capacitor, presumably because it accumulates charge, condensing it – like condensed milk?
Jacinta: Condensation in chemistry, or whatever, means transformation from a gas, or vapour, to a liquid. Remember they were thinking of an electrical fluid in the early days.
Canto: Well this excellent website on the early days tells me that the effect they were creating by rubbing a glass globe is now called the triboelectric effect. And by the way it was Franklin who worked out that it was the glass that was creating the effect – nout to do with water, it seems.
Jacinta: Yes, it’s an everyday effect – you can get it just through combing your hair, or rubbing a plastic pen on your sleeve and then picking up bits of paper. I did it at school! I was very sciencey in them days.
Canto: Interestingly, there are lots of nice comments on this website, pointing out that the term for capacitor in a number of European languages is kondensator, or variants thereof. But we get yet another story here on early Leyden jars, which I’ll need to unpick:
It was realized also at Leyden University that it worked only if the glass container was held in your hand and not if it was supported by an insulating material. Today we realize that the alcohol or water in contact with the glass was acting as one plate of the capacitor and the hand was acting as the other while the glass was the dielectric. The high voltage source was the friction machine and the hand and body provided a ground.
Jacinta: So sometimes water was used as a ‘plate’ instead of the tin foil on the inner surface, and the hand was acting as the other plate. So, different versions of Leyden jars. And the dielectric? Yet another unexplained term.
Canto: Yeah, they just never simplify things enough for fuckwits like us. A dielectric is apparently an insulator. Or, as Wikipedia expands it, it’s ‘an electrical insulator that can be polarised by an applied electric field’. Now, I thought that an insulator was the opposite of a conductor, that it tends to be a bad conductor, something that’s difficult for a charge to pass through. Or is that a resistor? Anyway, I can see how dielectric, meaning two, has to do with polarisation, positive and negative, but it still remains vague. I just thought an insulator kind of protects people from getting electric shocks.
Jacinta: So, going back to Crump, here’s a quote:
Franklin succeeded in giving Leyden jars both positive and negative charges, and showed that the force itself was stored in the glass of the jar with the charge being proportional to its surface area.
I DO NOT UNDERSTAND THIS. I WANT TO UNDERSTAND. Does he mean positive and negative charges at the same time? Is that what a dielectric is? And when he says the force was stored in the glass, and the charge bore a mathematical relation to the surface area of the glass, does he mean a different thing by force and charge? And if the charge is proportional to the surface area of the glass, does that mean that if the surface area of the glass was equal to, say, the surface area of a glassy planet Earth, you’d get a more than respectable charge? And if our universe has a surface area?
Canto: The universe isn’t made of glass, I learned that from Dava Sobel’s The glass universe. Or not.
Jacinta: Okay, let me look up some common definitions before we go on.
A dielectric is a material that transmits electricity without conducting. That’s to say, an insulator (BUT I DON’T UNDERSTAND WHAT THIS MEANS). Examples of dielectric materials include glass, ceramics, metallic oxides, plastics and dry air.
An insulator, electrically speaking, is a material in which electricity can’t flow freely. In such materials, electrons are tightly bound – though it’s all relative. They’re said to be resistive. So presumably there’s a connection between resistors and insulators. Most insulators are non-metals.
A conductor is a material that allows a flow of electrrical charge, aka a current. Metals, such as copper wire, are commonly used as conductors.
Electric charge – and I think this is really the biggie – is a state or property of matter when a certain force from an electromagnetic field is applied to it. Or when it is within an electromagnetic field. But we won’t try to define an electromagnetic field until part 30 or so. An electric charge can be positive (carried by protons) or negative (electrons). This is not, of course, a full definition.
Triboelectricity is a charge of electricity gained by friction. The triboelectric effect can be varied and unpredictable, depending on the precise structure of the materials being rubbed together.
A capacitor, originally called a condenser, a term first coined by Volta, is… well, we posted a piece over four years ago called ‘What are capacitors?’ – but we’ve never thought about them since…
Canto: Yes, I’ve skimmed through that piece and I barely understand it. Let’s just say for now that a capacitor is a device for temporarily storing electricity, but that it differs from a battery somehow.
Jacinta: Okay, one more term used in Hackaday’s ‘History of the capacitor’ that needs explaining is hygroscopic. It says that soda glass, whatever that is, is hygroscopic. Franklin used soda glass in his experiments, apparently.
Canto: Google only tells me something about soda-lime glass, which I’m hoping is the same thing. It’s the most prevalent type of glass, composed of 70% silicon dioxide, or silica, 15% soda (sodium dioxide) and 9% lime (calcium oxide). The other 6% is made up of ‘other’. Hygroscopic materials attract water molecules from the surrounding environment, either by absorption or adsorption, but Wikipedia, which gives a large list of hygroscopic materials, makes no mention of glass or silicon as hygroscopic, though it does mention sodium salts.
Jacinta: So let’s move on with the history of these electrical discoveries, and maybe we’ll solve the problem of our own ignorance along the way. I note that potted histories of the battery, such as the one I’m about to quote from, don’t bother to distinguish between a battery and a capacitor:
Ben Franklin built an electric battery using glass window panes and thin lead plates. Using his “electric battery,” a term he coined himself, he showed how electricity could be stored in the glass and passed through it. Shouldn’t we call it the great-grand-dad of electric batteries?
So let’s not worry about it, though I suspect Yank jingoism is at play here. Let’s move on to Alessandro Volta.
Canto: And the continuous current battery. Volta’s first contribution to electricity was to improve on the electrophorus…
Jacinta: And here’s a great definition of the electrophorus, a device actually named by Volta:
An electrophorus or electrophore is a simple manual capacitive electrostatic generator used to produce electrostatic charge via the process of electrostatic induction.
Canto: Clear as mud. An electrophorus apparently consists of a dielectric plate…
Jacinta: Yeah, something that transmits electricity without conducting it.
Canto: Okay, let’s clear that up – perhaps. Dielectric materials don’t have free electrons for conducting electricity – they’re insulators. Electrons are, of course, electrically charged particles, and in dielectrics they’re tightly bonded to their nuclei. What does happen when an electric field or current is applied is that they become polarised. This raises the question of what polarisation actually is, and what it is about an electric field/current that causes this polarisation.
Jacinta: Not to mention whether there is a difference between an electric field and an electric current.
Canto: Okay, more work to be done. There are different types of polarisation. The polarisation of light, for example, is a complex story which we’ll have to deal with in another 50,000 part series. But here’s a general description from Britannica:
polarization, property of certain electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified way.
So, just off the top of my head, an electric current seems to imply direction, whereas electric field not so much. On electric polarisation, ScienceDirect, which takes material from scientific papers, has this:
Electric polarization refers to the separation of center of positive charge and the center of negative charge in a material. The separation can be caused by a sufficiently high-electric field.
I think this means that dielectrics can be separated in terms of overall positive and negative charge in their individual atomic make-up, so that they can become magnetised, sort of? Because I think of magnetism in terms of polarity. They can become polarised, like magnets, while not being able to conduct an electric charge. Maybe.
Canto: We seem to have come a long way from capacitors.
Jacinta: We got lost on electrophoruses. An electrophorus consists of a dielectric plate..
Canto: Okay, here’s another definition, from Oxford Reference:
An early form of electrostatic generator. It consists of a flat dielectric plate and a metal plate with an insulated handle. The dielectric plate is charged by friction and the metal plate is placed on it and momentarily earthed, which leaves the metal plate with an induced charge of opposite polarity to that of the dielectric plate. The process can be repeated until all of the original charge has leaked away.
Jacinta: So this gives me a visible image, of sorts. The flat dielectric plate – and I assume a plate is something flat and thin – is polarised by friction, and a metal plate, that’s to say a conductor, is brought into contact with it and then momentarily earthed (I DON”T UNDERSTAND THIS), which leaves an induced charge of opposite polarity on this other plate )I DON”T UNDERSTAND THIS EITHER), and with repetition the original charge is leaked away (DITTO).
Canto: It seems every explanation needs further explanation, and we’re constantly changing electricity’s tail. And we’ve only just begun 🎵.
References
https://en.wikipedia.org/wiki/Triboelectric_effect
https://en.wikipedia.org/wiki/Hygroscopy
https://www.britannica.com/technology/soda-lime-glass
https://www.britannica.com/science/polarization-physics
https://www.oxfordreference.com/view/10.1093/oi/authority.20110803095746578
what is electricity? part 2 – the mystery gets murkier
Canto: So we were trying to comprehend early ideas about electricity as a fluid, which led Franklin to define two ‘states’ of the fluid, ‘negative’ for having a deficiency, and ‘positive’ for having an excess. He also called the negative state ‘resinous electricity’ and its opposite ‘vitreous electricity’. Presumably he thought the fluid was in a balanced state before these different elements started rubbing against each other.
Jacinta: And they were trying to regain this balanced state, which made the sparks fly?
Canto: Dunno, but let’s return to Britain, where Francis Hauksbee (1660-1713), a lab assistant to Isaac Newton, was being inventive with air pumps and pneumatic engines, decades before Franklin’s 1840s experiments.
Jacinta: I’d ask you what a pneumatic engine is, but I suppose that’d take us way off topic?
Canto: Probably. It apparently has something to do with compressed air, and some kind of energy derived from un-compressing it, or something. Anyway, air pumps were used to create vacuums, or relative vacuums. Apparently, Hauksbee, an ingenious instrument maker, noted that glass was a really good material for viewing experiments, and in 1705 he performed a remarkable experiment with one of his air pumps and that mercurial, and very dangerous element, mercury (though ‘elements’ in the modern sense, weren’t known or at least defined at the time).
Jacinta: I suppose elements wouldn’t have been defined until the atomic theory became a thing.
Canto: Anyway I’m betting that his experiments with mercury shortened Hauksbee’s poor life (he was accepted into the Royal Academy in 1703, just as Newton became its president with the aim of reinstating its grandeur, but he was given special ‘low class’ status). He’d created a version of Otto von Guericke’s electrical machine, made of glass, with air pumped out, and some mercury inside. He rubbed the sphere to create a charge, and the mercury glowed when he put his hand on it (the globe, not the mercury). Fantastical, but nobody knew what it meant, except that it could be used as a source of night-light, which actually happened, but much later.
Jacinta: But nobody had much idea about whys and wherefores at this time.
Canto: They presumably speculated. A similar phenomenon, in large, was St Elmo’s fire (he was the patron saint of sailors), a bluish glow around a sailing ship, or more recently, around an aircraft. We know now this is a form of plasma, the ionised state of matter. During thunderstorms the voltage differentials are greatest – it requires a particular differential for it to happen, and the shape of the body around which the light is seen is an important factor. Pointy objects create a more intense field (Franklin realized this). The violet-blue light is caused by the nitrogen and oxygen in the atmosphere.
Jacinta: Are you sure you know what you’re talking about?
Canto: I’m never certain about anything, that’s my vocation, or just my fate.
Jacinta: Pneumatic tyres are filled with compressed air, or gas. So that helps to understand what a pneumatic engine might be, maybe.
Canto: So Hauksbee had found a way to accumulate an electric charge, and in 1745, in Leyden, Holland, they found a way to store this charge – an instrument that came to be known as a Leyden jar. Let me quote from the scientific historian, Thomas Crump:
The so-called Leyden jar was simply a substantial glass chamber, with separate layers of metal foils on the inside and outside surfaces. The inside was charged by a metal chain connecting it to a charged body, which then lost its charge to the air.
And this was apparently the first capacitor. We’ve talked about capacitors and supercapacitors before, but of course we barely understand them. In any case this Leyden jar device allowed a lot of electrostatic potential to build up between the inner and outer surfaces – enough to kill small birds who came in contact. Nice.
Jacinta: Or were forced to come into contact. I know they tried it on monks too. Presumably they couldn’t find the nuns.
Canto: Anyway they now had some control over this electricity thing, even if they hadn’t a clue what it was. They had some idea as to how to create and release this electrical charge thingummy.
Jacinta: So now we come to Coulomb?
Canto: No, Alessandro Volta (1745-1827) first. I’m following Crump, for better or worse. But more importantly than people, it’s batteries we’re going to focus on now. And I’m not sure where to begin.
Jacinta: It was a term – battery I mean – first used by Franklin in 1749, but what he actually created were capacitors, devices that accumulated charge, until they were discharged. Batteries – I’m kind of guessing here – are devices that store charge more or less permanently, and can release charge in a controlled way, and be recharged in a controlled way.
Canto: And what is this thing called charge?
Jacinta: Well let’s continue to grope toward an understanding. So I’ll return to Franklin. He wrote a book, Experiments and observations on electricity, made at Philadelphia in America, published in 1751. His researches led him to believe that everything contained charge, positive and negative, but that they were almost always in equilibrium, a neutral state. Or the fluid, which could be ‘negativised’ or ‘positivised’ by friction, could be returned to balance by ‘discharging’ it.
Canto: And surely therein lay a mystery. How or why did this build-up of negativity or positivity get discharged? I just don’t understand it. Not just the discharge but the creation of the charge.
Jacinta: I suppose they – Franklin, Hauksbee and the rest – just made the observation and called it ‘charge’. From whence, ‘discharge’. Maybe you’re just overthinking it. They certainly didn’t know what was going on, they just noted this reliable cause-and-effect behaviour and sought to utilise it, and find out more about it. Anyway, keep on overthinking, it might be a good thing.
Canto: Okay, Franklin was exercised by the discharge side of things. He found that pointy objects – we now call them lightning conductors – were most effective at discharging this build-up of charge, and recreating neutrality, the safe, ‘natural’ condition. A great, practical solution for buildings. But he developed a theory of sorts, of zero-sum conservation of this thing called charge. Whatever was accumulated in, say, a Leyden jar, was restored on discharge, nothing gained and nothing lost. I think.
Jacinta: Well, here’s a quote from Crump’s book, which might unenlighten us further:
Franklin succeeded in giving Leyden jars both positive and negative charges, and showed that the force itself was stored in the glass of the jar with the charge being proportional to its surface area.
Canto: Yeah, that needs unpacking, if possible. The ‘force’ being stored, is that the charge? If so, why does he use different terms? Charge is either negative or positive, isn’t it? So he was able to give these jars either a negative or a positive charge/force, but not both at the same time, though it’s ambiguous in this quote.
Jacinta: What I think he’s saying is there’s this force, which we now call electricity, which can either be negatively or positively charged, and its strength will be proportional to the surface area of the glass jar. I don’t think he was giving the jar different charges at the same time, but how he knew that the charge was sometimes positive, sometimes negative, or what that even means, I’ve no idea.
Canto: Yes, I’m more confused than ever. Let’s try to understand Leyden jars a bit more. Apparently it was invented in 1745 by one Pieter van Musschenbroek as a ‘cheap and convenient source of electric sparks’. That’s from Britannica on electromagnetism. So, to be more precise about this first jar, it was a glass vial partially filled with water, which ‘contained a thick conducting wire capable of storing a substantial amount of charge’.
Jacinta: Presumably that ‘thick conducting wire’ corresponds to the ‘metal chain’ in Crump’s description. I don’t know what the water’s for.
Canto: And Britannica makes no mention of the ‘separate layers [how many???!!] on the inside and outside surfaces’.
Jacinta: Okay, here’s a simplified picture, which might help.
So, in this one there’s no water, but I’ve seen other pics that indicate a jar more than half-filled with water, so who fucking knows. Note that there’s one layer of tin foil on the outside and another on the inside. Note the metal rod passing through a cork into this evacuated jar, and then a wire, presumably of some kind of metal, connecting to the tin foil.
Canto: Is tin a good conductor?
Jacinta: Apparently so. Not as good as silver or copper, but better than lead. And please don’t ask me why some metals are better conductors than others. It’s so frustrating trying to learn from the internet, even when you know which sites to avoid. For example, take this statement on what I’d expect to be a reliable site:
Although Leyden Jars allowed the storage and dissipation of electricity, there were still issues present. One issue was the lack of energy from the charge. While it could only attract small objects like a bit of paper, that was all it could basically do. Also, it could only perform that function after the jar was charged, which also took lots of time.
And then this, from Britannica:
The Leyden jar revolutionized the study of electrostatics. Soon “electricians” were earning their living all over Europe demonstrating electricity with Leyden jars. Typically, they killed birds and animals with electric shock or sent charges through wires over rivers and lakes. In 1746 the abbé Jean-Antoine Nollet, a physicist who popularized science in France, discharged a Leyden jar in front of King Louis XV by sending current through a chain of 180 Royal Guards. In another demonstration, Nollet used wire made of iron to connect a row of Carthusian monks more than a kilometre long; when a Leyden jar was discharged, the white-robed monks reportedly leapt simultaneously into the air.
Canto: Hmmm. One of these descriptions is not like the other. Where’s Micky Faraday when you need him?
Jacinta: I can but do my best. Let’s get back to batteries, again. Franklin’s ‘battery’ was really a capacitor, as mentioned, a way of accumulating more electric charge, and temporarily storing it, until it was required for a sort of ‘big bang’ release, I think. You can do this with Leyden jars linked together:
The above ‘device’ was used for demonstration purposes back in the day. Franklin’s electrostatic machine, though, didn’t look anything like this. It was a mammoth device of cranks and pulleys, created with much help from his friends. The mechanisation was presumably for creating as great an accumulation of charge as possible. Crump writes that Franklin built a glass and lead battery consisting of eleven condensers connected in series – which is clearly not his electrostatic machine. And apparently it wasn’t a battery, either, at least not in the modern sense. And WTF is a condenser? Anyway, this confusion has gone on long enough. We’ll try to clear some of it up next time.
References
Thomas Crump, A brief history of science
https://en.wikipedia.org/wiki/Francis_Hauksbee
https://en.wikipedia.org/wiki/St._Elmo%27s_fire
https://www.britannica.com/science/electromagnetism/Invention-of-the-Leyden-jar
https://www.bluesea.com/resources/108/Electrical_Conductivity_of_Materials
https://en.wikipedia.org/wiki/Franklin%27s_electrostatic_machine
what are capacitors?
the shapes and sizes of capacitors – a screenshot taken from the youtube vid – What are Capacitors? – Electronics Basics 11
Jacinta: We’re embarking on the clearly impossible task of learning about every aspect of clean (and sometimes dirty because nothing’s 100% clean or efficient) technology – batteries, photovoltaics, turbines, kilo/megawatt-hours, glass electrolytes, powerwalls, inverters, regen, generators, airfoils, planetary gear sets, step-up transformers, nacelles AND capacitors.
Canto; Enough to last us a lifetime at our slow pace. So what, in the name of green fundamentalism, is a capacitor?
Jacinta: Well I’ve checked this out with Madam Youtube…
Canto: Professor Google’s co-dependent…
Jacinta: And in one sense it’s simple, or at least it sounds simple. Capacitors store electric charge, and the capacitance of a capacitor relates to how much charge it can hold.
Canto: So how does it do that, and what’s the purpose of storing electric charge?
Jacinta: Okay now you’re complicating matters, but basic to all capacitors are two separated pieces of conducting material, usually metal. Connected to a battery, they store charge…
Canto: Which is a kind of potential energy, right?
Jacinta: Umm, I think so. So take your battery with its positive and negative terminals. Attach one of the bits of conducting material (metal) to the positive terminal and you’ll get a flow of negatively-charged electrons to that terminal, because of ye olde law of attraction. This somehow means that electrons are repelled from the negative terminal (which we’ve hooked up to the other bit of metal in the capacitor). So because the first strip of metal has lost electrons it has become positively charged, and the other bit of metal, having gained electrons, has an equal and opposite charge. So each piece of metal has the same magnitude of charge, measured in coulombs. This is regardless of the size and shape of the different metal bits.
Canto: But this process reaches a limit, though, yes? A kind of saturation point…
Jacinta: Well there comes a point where, yes, the accumulated charge just sits there. This is because there comes a kind of point of equilibrium between the positive battery terminal and the now positively charged strip of metal. The electrons are now caught between the attractive positive terminal and the positive strip.
Canto: Torn between two lovers, I know that foolish feeling.
Jacinta: So now if you remove the battery, so breaking the circuit, that accumulated charge will continue to sit there, because there’s nowhere to go.
Canto: And of course that accumulated or stored charge, or capacitance, is different for different capacitors.
Jacinta: And here’s where it gets really complicated, like you know, maths and formulae and equations. C = Q/V, capacitance equals the charge stored by the capacitor over the voltage across the capacitor. That charge (Q), in coulombs, is measured on one side of the capacitor, because the charges actually cancel each other out if you measure both sides, making a net charge of zero. So far, so uncomplicated, but try and get the following. When a capacitor stores charge it will create a voltage, which is essentially a difference in electric potential between the two metal strips. Now apparently (and you’ll have to take my word for this) electric potential is high near positive charges and low near negative charges. So if you bring these two differently charged strips into close proximity, that’s when you get a difference in electric potential – a voltage. If you allow a battery to fully charge up a capacitor, then the voltage across it (between the two strips) will be the same as the voltage in the battery. The capacitance, Q/V, coulombs per volt, is measured in farads, after Micky Faraday, the 19th century electrical wizz. I’m quoting this more or less verbatim from the Khan Academy video on capacitors, and I’m almost finished, but here comes the toughest bit, maths! Say you have a capacitor with a capacitance of 3 farads, and it’s connected to a nine volt battery, the charge stored will be 27 coulombs (3 = 27/9). 3 farads equals 27 coulombs of charge divided by nine volts, or 27 coulombs of charge is 3 farads times 9 volts. Or, if a 2 farad capacitor stores a charge of 6 coulombs, then the voltage across the capacitor will be 3 volts.
Canto: Actually, that’s not so difficult to follow, the maths is the easiest part for me… it’s more the concepts that get me, the very fact that matter has these electrical properties…
Jacinta: Okay here’s the last point made, more or less verbatim, on the Khan Academy video, something worth pondering:
You might think that as more charge gets stored on a capacitor, the capacitance must go up, but the value of the capacitance stays the same because as the charge increases, the voltage across that capacitor increases, which causes the ratio to stay the same. The only way to change the capacitance of a capacitor is to alter the physical characteristics of that capacitor (like making the pieces of metal bigger, or changing the distance between them).
Canto: Okay so to give an example, a capacitor might be connected to an 8 volt battery, but its capacitance is, say, 3 farads. It will be fully charged at 24 coulombs over 8 volts. The charge increases with the voltage, which has a maximum of 8. The ratio remains the same. Yet somehow I still don’t get it. So I’m going to have a look at another video to see if it helps. It uses the example of two metal plates. They start out as electrically neutral. You can’t force extra negativity, in the form of electrons, into one of these plates, because like charges repel, and they’ll be forced out again. But, according to the video, if you place another plate near the first, ‘as electrons accumulate in the first metal plate, they will repel the electrons in the second metal plate’, to which I want to respond, ‘but electrons aren’t accumulating, they’re being repelled’. But let’s just go with the electron flow. So the second metal plate becomes depleted of electrons and is positively charged. This means that it will attract the negatively charged first metal plate. According to the video, this makes it possible for the first plate to have more negative than positive particles, which I think has something to do with the fact that the electrons can’t jump from the first plate to the second, to create an equilibrium.
Jacinta: They’re kind of attracted by absence. That’s what they must mean by electric potential. It’s very romantic, really. But what you’ve failed to notice, is that a force is being continually applied, to counteract the repulsion of electrons from the first plate. If the force no longer applies then, yes, you won’t get that net negative charge in the first plate, and the consequent equal and opposite charge in the second. My question, though, is how can the capacitance increase by bringing the plates closer together? I can see how it can be changed by the size of the conducting material – more electrons, more electric potential. I suppose reducing the distance will increase the repulsive force…
Canto: Yes, let’s assume so. Any, a capacitor, which stores far less charge than a similarly-dimensioned battery can be used, I think, to briefly maintain power to, say, a LED bulb when it is disconnected from the battery. The capacitor, connected to the bulb will discharge its energy ‘across’ the bulb until it achieves equilibrium, which happens quite quickly, and the bulb will fade out. If the capacitor is connected to a number of batteries to achieve a higher voltage, the fully charged capacitor will take longer to discharge, keeping the light on for longer. If the metal plates are larger, the capacitor will take longer to charge up, and longer to discharge across the LED bulb. Finally, our second video (from a series of physics videos made by Eugene Khutoryansky) shows that you can place a piece of ‘special material’ between the two plates. This material contains molecules that change their orientation according to the charges on the plates. They exert a force which attracts more electrons to the negative plate, and repel them from the positive plate, which has the same effect as increasing the area of the plates – more charge for the same applied voltage.
Jacinta: An increase in capacitance.
Canto: Yes, and as you’ve surmised, bringing the two plates closer together increases the capacitance by attracting more electrons to the negatively charged plate and repelling them from the positively charged one – again, more charge for the same voltage.
Jacinta: So you can increase capacitance with a combo of the three – increased size, closer proximity, and that ‘special material’. Now, one advantage of capacitors over batteries is that they can charge up and discharge very quickly. Another is that they can endure many charge-discharge cycles. However they’re much less energy dense than batteries, and can only store a fraction of the energy of a same-sized battery. So the two energy sources have different uses.
Canto: Mmmm, and we’ll devote the next post to the uses to which capacitors can be put in electronics, and EVs and such.